project-swan/libswan/include/swan/util.h

#pragma once

#include <optional>
#include <functional>
#include <memory>
#include <chrono>
#include <type_traits>
#include <string>
#include <cstddef>
#include <cstdint>

namespace Swan {

inline uint32_t random(uint32_t x) {
	x ^= 0x55555555u;
	x = ((x >> 16u) ^ x) * 0x45d9f3bu;
	x = ((x >> 16u) ^ x) * 0x45d9f3bu;
	x = (x >> 16u) ^ x;
	return x;
}

// Inherit from this class to make a class non-copyable
class NonCopyable {
public:
	NonCopyable(const NonCopyable &) = delete;
	NonCopyable(NonCopyable &&) noexcept = default;
	NonCopyable &operator=(const NonCopyable &) = delete;
	NonCopyable &operator=(NonCopyable &&) = default;

protected:
	NonCopyable() = default;
	~NonCopyable() = default;
};

// Take a deleter function, turn it into a class with an operator() for unique_ptr
template<typename T, void (*Func)(T *)>
class CPtrDeleter {
public:
	void operator()(T *ptr) { Func(ptr); }
};

// This is just a bit nicer to use than using unique_ptr directly
template<typename T, void (*Func)(T *)>
using CPtr = std::unique_ptr<T, CPtrDeleter<T, Func>>;

// Take a function, run it when the object goes out of scope
template<void (*Func)()>
class Deferred: NonCopyable {
public:
	Deferred() = default;
	~Deferred() { Func(); }
};

inline struct ResultOk {} Ok;
inline struct ResultErr {} Err;

// Result type for potential errors
template<typename T, typename Err = std::string>
class Result {
public:
	Result(ResultOk, T &&val): isOk_(true), v_(ResultOk{}, std::move(val)) {}
	Result(ResultErr, Err &&err): isOk_(false), v_(ResultErr{}, std::move(err)) {}

	Result(const Result &other): isOk_(other.isOk_) {
		if (isOk_) {
			new (&v_.val) T(other.v_.val);
		} else {
			new (&v_.err) T(other.v_.err);
		}
	}

	Result(Result &&other): isOk_(other.isOk_) {
		if (other.isOk_) {
			new (&v_.val) T(std::move(other.v_.val));
		} else {
			new (&v_.err) Err(std::move(other.v_.err));
		}
	}

	~Result() {
		destroy();
	}

	Result<T, Err> &operator=(const Result<T, Err> &other) {
		destroy();
		isOk_ = other.isOk_;
		if (isOk_) {
			new (&v_.val) T(other.v_.val);
		} else {
			new (&v_.err) Err(other.v_.err);
		}
		return *this;
	}

	Result<T, Err> &operator=(Result<T, Err> &&other) {
		destroy();
		isOk_ = other.isOk_;
		if (other.isOk_) {
			new (&v_.val) T(std::move(other.v_.val));
		} else {
			new (&v_.err) Err(std::move(other.v_.err));
		}
		return *this;
	}

	explicit operator bool() { return isOk_; }
	bool isOk() { return isOk_; }

	Err &err() { return v_.err; }
	T &value() { return v_.val; }

	T *operator->() {
		return &v_.val;
	}

	T &operator*() {
		return v_.val;
	}

private:
	void destroy() {
		if (isOk_) {
			v_.val.~T();
		} else {
			v_.err.~Err();
		}
	}

	bool isOk_;
	union U {
		U() {}
		U(ResultOk, T &&val): val(std::move(val)) {}
		U(ResultOk, const T &val): val(val) {}
		U(ResultErr, Err &&err): err(std::move(err)) {}
		U(ResultErr, const Err &err): err(err) {}
		~U() {}
		T val;
		Err err;
	} v_;
};

// Calling begin/end is stupid...
template<typename T>
auto callBegin(T &v) {
	using namespace std;
	return begin(v);
}
template<typename T>
auto callEnd(T &v) {
	using namespace std;
	return end(v);
}

// Ret can't be a reference, because C++ doesn't support optional<T&>.
template<typename Ret, typename Func = std::function<std::optional<Ret>()>>
class Iter {
public:
	class It {
	public:
		It(std::optional<Ret> next, Func &func): next_(std::move(next)), func_(func) {}

		bool operator==(const It &other) const {
			return next_ == std::nullopt && other.next_ == std::nullopt;
		}

		bool operator!=(const It &other) const {
			return !(*this == other);
		}

		void operator++() {
			auto val(func_());
			if (val)
				next_.emplace(std::move(*val));
			else
				next_.reset();
		}

		Ret operator*() {
			return std::move(*next_);
		}

	private:
		std::optional<Ret> next_;
		Func &func_;
	};

	Iter(Func func): func_(func) {}

	operator Iter<Ret, std::function<std::optional<Ret>()>>() {
		return Iter<Ret, std::function<std::optional<Ret>()>>(func_);
	}

	It begin() {
		return It(func_(), func_);
	}

	It end() {
		return It(std::nullopt, func_);
	}

private:
	Func func_;
};

template<typename InputIterator, typename Func>
auto map(InputIterator first, InputIterator last, Func func) {
	using RetT = decltype(func(*first));

	auto l = [=]() mutable -> std::optional<RetT> {
		if (first == last)
			return std::nullopt;

		RetT r = func(*first);
		++first;
		return r;
	};

	return Iter<RetT, decltype(l)>(l);
}

template<typename Range, typename Func>
auto map(Range &rng, Func func) {
	return map(callBegin(rng), callEnd(rng), func);
}

template<typename InputIterator, typename Func>
auto filter(InputIterator first, InputIterator last, Func pred) {
	using RetT = std::remove_reference_t<decltype(*first)>;

	auto l = [=]() mutable -> std::optional<RetT> {
		if (first == last)
			return std::nullopt;

		while (!pred(*first)) {
			++first;
			if (first == last)
				return std::nullopt;
		}

		RetT r = *first;
		++first;
		return r;
	};

	return Iter<RetT, decltype(l)>(l);
}

template<typename Range, typename Func>
auto filter(Range &rng, Func func) {
	return filter(callBegin(rng), callEnd(rng), func);
}

template<typename InputIterator, typename Func>
auto mapFilter(InputIterator first, InputIterator last, Func func) {
	using RetT = std::remove_reference_t<decltype(*func(*first))>;

	auto l = [=]() mutable -> std::optional<RetT> {
		if (first == last)
			return std::nullopt;

		std::optional<RetT> r;
		while ((r = func(*first)) == std::nullopt) {
			++first;
			if (first == last)
				return std::nullopt;
		}

		++first;
		return r;
	};

	return Iter<RetT, decltype(l)>(l);
}

template<typename Range, typename Func>
auto mapFilter(Range &rng, Func func) {
	return mapFilter(callBegin(rng), callEnd(rng), func);
}

}